This invention relates to the field of axial flow rotary machines and more particularly to a method and detail for processing, modifying or repairing a stator vane.
FIG. 1 shows an axial flow rotary machine 10 of the turbofan, gas turbine engine type. The engine includes a compression section 12, a combustion section 14, and a turbine section 16 which are disposed an axis A. An annular flowpath 18 for working medium gases extends through the sections of the engine. The annular flowpath is the primary flowpath for the turbofan engine.
The working medium gases are compressed in the compression section 12. The compressed gases are mixed with fuel in the combustion section 14 and burned to add energy to the gases. The hot pressurized gases are expanded through the turbine section 16 to produce useful work and are discharged from the engine to produce thrust.
As shown in FIG. 1 and FIG. 2, the engine is provided with a rotor assembly 22 In the turbine section 16. The rotor assembly includes a rotor disk 24 and arrays of rotor blades which extend outwardly across the working medium flowpath, as represented by the arrays of rotor blades 26. The rotor assembly extracts energy from the gases as the gases are passed through the turbine section. The rotor assembly transfers this energy to the compression section 14 to compress the incoming working medium gases.
A stator assembly 28 extends circumferentially about the rotor assembly 22. The stator assembly supports the rotor assembly and includes a pressure vessel, as represented by the outer case 32, to confine the working medium gases to the working medium flowpath. In many embodiments, the outer case also provides a support structure for components which bound the working medium flowpath. The stator assembly includes arrays of stator vanes 34 interdigitated with the arrays of rotor blades. Each array of stator vanes is disposed about the axis A.
As shown in FIG. 2, each stator vane 34 extends circumferentially with respect to the axis A. Each stator vane typically has an inner platform 36 and an outer platform 38. The stator vane has an upstream end 42 and a downstream end 44. These ends are also called respectively the leading edge and the trailing edge of the stator vane. An upstream leg 46 and a downstream leg 48 extend radially from the outer platform. Each leg has a foot, as represented by the upstream foot 52 and by the downstream foot 54. Each foot adapts the leg to engage the outer case. One or more airfoils 56 extend radially across the working medium flowpath between the inner platform and the outer platform. The term xe2x80x9cstator vanexe2x80x9d includes constructions which have one airfoil or several airfoils. Stator vane constructions having several airfoils are frequently called xe2x80x9cstator vane clustersxe2x80x9d.
The airfoil 56 of the stator vane extends spanwisely and has a pressure side 58 and a suction side 62 (shown in FIG. 3). The sides guide the working medium gases as the gases exit one array of rotor blades and enter a downstream array of rotor blades. The working medium gases push against and buffet the airfoil exerting both steady and unsteady aerodynamic forces on the airfoil. These forces are in part the result of wakes from the upstream rotor blades and bow waves from downstream rotor blades. In addition, heat is transferred from the hot working medium gases to the stator vane 34 and particularly to the airfoils 56. The heat causes thermal gradients in the stator vane. The thermal gradients are aggravated by circumferential variations in temperature of the working medium gases in the flowpath. These variations in temperature result from variations in upstream operating conditions at the combustion section 14 of the engine.
The aerodynamic and thermal forces cause cyclic stresses in the stator vane 34 and may cause cracking of the stator vane, for example, at those locations on the airfoil 56 that are subjected to high repetitive stresses. The leading edge 64 of the airfoil 56 is one location on the stator vane that is particularly vulnerable to cracking. This occurs because the airfoil is a structural beam that has a very narrow outermost fiber, that is, the relatively narrow leading edge 64. The narrow leading edge of the beam has an associated high stress concentration factor. The effect of this high stress concentration factor is aggravated by the change in geometry at the location where the airfoil (or structural beam) transitions into the outer platform 38 and is referred to as the region or junction T. This is usually the tangency point between the airfoil fillet and the airfoil.
FIG. 3 is a perspective view of three stator vanes 34. Each stator vane has three airfoils 56. FIG. 4 is a cross-sectional view of the pressure side airfoil 56 with part of the airfoil broken away. As shown in FIG. 3 and FIG. 4, cracking of the pressure side airfoil 56 frequently occurs in the leading edge 64 at the junction T, that is, the transition from the leading edge of the airfoil to the platform. With time, the crack will grow rearwardly from the leading edge and may lead to destructive failure of the stator vane. Depending on its circumferential location in the annular flowpath 18 with respect to upstream operating conditions, the stator vane may not have a cracked pressure side airfoil as shown. Instead or in addition to the pressure side airfoil, the central airfoil or suction side airfoil may crack at the leading edge. Typically, none of these stator vanes are repairable by welding or bonding repairs, such as by using diffusion bonding filler, because of the high stress concentration factors acting at the transition of the leading edge to the platform.
One approach is to replace damaged stator vanes with redesigned stator vanes. FIG. 5 is a schematic, side elevation view of a redesigned stator vane 34r which is partially in section and partially broken away. The redesigned stator vane has a leg 46r having an axial thickness or axial length D. This thickness is uniform for the entire circumferential extent of the redesigned stator vane. The thickness of the redesigned stator vane is thicker or longer in the axial direction than the thickness or axial length D of the upstream leg 46 shown in FIG. 3 and FIG. 4. The redesigned stator vane 34r has a local opening or local pocket 66 at each airfoil 56r which extends rearwardly from the upstream end 42 of the stator vane. The opening is circumferentially and axially aligned with the leading edge 64r of the airfoil. The opening interrupts the radial continuity of the stator vane and the radial continuity of the load path from the airfoil leading edge to the leg and thence to the support structure. This causes the load path to shift rearwardly. The high gas loads acting on the airfoil are not passed by the stator vane through the leading edge region next to the platform. This avoids subjecting the loads to the high stress concentration factor caused by the narrow leading edge and the transition geometry. As a result, the stator vane has an increased fatigue life. However, replacing an earlier version of the stator vane that is cracked or expected to crack with a redesigned stator vane requires the purchase of a new stator vane.
Accordingly, scientists and engineers working under the direction of applicants assignee have sought to develop a method for processing a stator vane which has a crack or which might crack in a critical location such as the transition zone from the leading edge to the platform.
This invention is in part predicated on the recognition that earlier version stator vanes may be modified or repaired by shifting the diffusion bonding surfaces for a replacement detail away from the leading edge to platform transition and its high concentration stress factor and forming a replacement detail having entirely new material at the junction T between the leading edge and the platform. Such a replacement detail may be used for a cracked or about to crack stator vane and may be bonded to the stator vane.
According to the present invention, a method for processing a stator vane includes removing part of the platform and leading edge region of the airfoil to remove the junction T of the leading edge and the airfoil and to form bonding surfaces on the airfoil and platform that are spaced from the junction; installing a replacement detail having bonding surfaces on an airfoil section and on a platform section that face the surfaces formed on the stator vane; and, bonding the replacement detail to the stator vane.
In accordance with one embodiment of the present invention, the method includes forming at least one bonding surface on the airfoil that faces in a generally axial direction and at least two bonding surfaces on the platform, with one facing in a generally axial direction and one facing in a generally circumferential direction.
In accordance with one embodiment of the present invention, the method includes forming surfaces on the platform that face toward each other in a generally circumferential direction.
In accordance with one embodiment of the present invention, the method is used for repairing a stator vane having a crack adjacent the junction T between the leading edge and the platform, the step of removing part of the airfoil includes removing all material bounding the crack and the step of installing a replacement detail includes replacing material at the location of the crack with new material.
In accordance with one embodiment of the present invention, the step of removing part of the stator vane includes forming at least one flat surface on the airfoil and on the airfoil section of the replacement detail and urging the surfaces together as the surfaces are bonded to each other.
In accordance with one embodiment of the present invention, the step of bonding the replacement detail includes disposing a layer of foil material between the surfaces on the airfoil and airfoil section and diffusion bonding the airfoil surfaces together and includes disposing a flowable bonding material between the platform surfaces for bonding the platform surfaces together.
In accordance with one embodiment of the present invention, the step of forming bonding surfaces on the airfoil and the platform comprises forming flat surfaces that are oriented such that planes containing platform surfaces on the stator vane are perpendicular to a plane containing the airfoil surface on the stator vane and the plane containing the airfoil section of the replacement detail in the installed condition. Planes are considered perpendicular if a line in one plane is perpendicular to any line in the other plane.
In accordance With one embodiment of the present invention, the step of removing material from the stator vane includes removing a portion of the leg extending from the platform and forming surfaces on the leg facing toward each other in a generally circumferential direction.
According to the present invention, a replacement detail for a stator vane has an airfoil section and a platform section and has at least three bonding surfaces with one located on an airfoil and facing in a generally axial direction and with two on a platform section of which at least one faces in a generally circumferential direction.
In accordance with one embodiment of the present invention, the platform has two bonding surfaces facing in opposite circumferential directions.
In accordance with one embodiment of the present invention, the replacement detail has flat surfaces such that a plane containing the airfoil section of the replacement detail is perpendicular to a plane containing at least one of the platform surfaces.
In accordance with one embodiment, the axially facing surface on the airfoil section of the replacement detail extends rearwardly from the leading edge toward the platform section leaving an acute angle between the surface and the leading edge to shift the airfoil bonding surfaces away from the junction between the platform and the leading edge of the airfoil.
In accordance with one embodiment, the replacement detail has a leg section extending in a generally radial direction from the platform section, the leg section cooperating with adjacent structure to support and position the upstream end of the stator vane; and, the replacement detail has an opening which is axially aligned with the leading edge of the airfoil for interrupting the radial continuity of the replacement detail to shift the load bearing path through the leg in the installed condition to a location on the platform which is axially rearward of the junction between the platform and the leading edge of the airfoil.
According to the present invention, a stator vane includes a platform, at least two airfoils extending from the platform, and an upstream leg for supporting the platform and airfoils, and further includes a section of the leg adjacent one of the airfoils which has an axial depth that is greater than the adjacent portion of the leg and includes an opening which interrupts the radial continuity of the cluster through the leg to the leading edge of the airfoil to decrease the load on the cluster at the junction between the leading edge and the platform.
According to the present invention, the stator vane has a replacement detail having at least three sections attached to the vane: a platform section, an airfoil section extending from the flowpath face of the platform, and a leg section which extends from the other face of the platform.
A primary feature of the method for processing a stator vane is the step of removing the junction between the leading edge of the airfoil and the platform. Another feature of the method is forming bonding surfaces which are spaced from the junction of leading edge with the platform. Still another feature is the step of bonding airfoil surfaces to join the replacement detail to the stator vane using pressure at the airfoil surfaces and using a flowable bonding material for platform surfaces that face circumferentially. In one embodiment, a feature is forming flat bonding surfaces for this circumferentially and axially facing surfaces on the platform and the axially facing surface on the airfoil.
A primary feature of the present invention is a replacement detail having an airfoil section and a platform section. The replacement detail has a junction at the leading edge of the airfoil section with the platform section. In one embodiment, the replacement detail has flat bonding surfaces which face in the axial direction and the circumferential direction. In one detailed embodiment, the replacement detail has a leg section extending from the platform section and an opening which interrupts the radial continuity of the load path from the leg to the leading edge of the airfoil section. In one embodiment, the replacement detail is formed of a material which is stronger than the material removed from the stator vane.
A primary feature of the present invention is a stator vane having at least one airfoil extending radially from a platform. A leg extends radially from the platform which adapts to the stator vane to be supported from adjacent structure of the rotary machine. The leg has an axially thicker section than the remainder of the leg beneath the leading edge region of the airfoil. An opening extends axially into the stator vane to interrupt the radial continuity of the load path extending through the leg and platform to the leading edge of the airfoil.
A primary advantage of the present invention is the ease of processing an airfoil which results from removing the junction T between the leading edge and the platform for forming bonding surfaces for the replacement detail. In one embodiment, this includes forming an axial facing surface on an airfoil and a circumferentially facing surface on the platform to bond the replacement detail in place. The use of the surfaces so oriented permits diffusion bonding under pressure against the axial facing surface and permits use of a flowable diffusion-bonding medium for the circumferentially facing surfaces. The flowable bonding medium enters the region between the surfaces by capillary action. A particular advantage is the ease of processing a stator vane which results from forming flat surfaces for locating a replacement detail against the stator vane and then bonding the replacement detail in place.
A primary advantage of the present invention is the durability of the replacement detail and the processed stator vane which has bonding surfaces spaced from the junction of the leading edge with the platform. In one embodiment, the replacement detail has a flat inclined surface on the airfoil section of the replacement detail which moves the load path from the support to the airfoil rearwardly from the leading edge, avoiding a region having high stress concentration factor in the stator vane. Another advantage is the durability of the stator vane which results from replacing material at a high stress location with entirely new material. An advantage of the present invention is the durability of the stator vane having a replacement detail which has replaced a highly stressed region of the stator vane with new material and which is bonded in place at bonding surfaces which are spaced from the high stress concentration area at the junction of the leading edge of the airfoil with the platform. Still another advantage is the flexibility of design for the processed stator vane which results from using a replacement detail which may be formed of a different material or with a different contour.
The foregoing and other features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof as discussed and illustrated in the accompanying drawings.